The present invention relates to a corrugated resin tube suitable for, for example, radiator hoses of automobiles.
As radiator hoses of automobiles, rubber hoses have been generally used for such a reason that the rubber hoses can be flexibly bent into a shape fitted to the arrangement of an engine and a radiator and absorb the relative displacement of the engine and radiator due to vibration during driving automobiles.
However, the rubber hoses are heavy and hardly handled, and when these are connected to engines or radiators, it is required to fasten these with hose clamps, whereby there is a problem that operation efficiency for installation is poor.
On the other hand, plastic tubes made of a thermoplastic resin or the like have been known. Among them, one having a corrugated portion has been known wherein the cross section along its axial direction has an undulated and uneven configuration.
Such a plastic tube is advantageous in such a point that it is remarkably lighter than rubber hoses, whereby its handling properties are excellent, and that a resinous connector may be integrally molded at the end portion of the plastic tube by which the plastic tube can be attached to the pipe of the engine or radiator by one-touch operation. Therefore, the plastic tube is advantageous in view of its excellent operation efficiency for installation.
However, when the plastic tube having the corrugated portion is used as a radiator hose, there is a problem that the tube tends to elongate at the corrugated portion due to the temperature rise of a coolant and the increase of internal pressure. When the tube elongates, the absorption of displacement vibration as the function inherent to the corrugated portion is impaired, and the elongated tube may contact with other devices in an engine room and unwanted holes may be made, whereby no adequate reliability can be obtained.
In order to solve this problem, tubes having a structure such that the ridges of corrugated portion are partly collapsed or adjacent ridges of corrugated portion are partly connected, have been proposed. However, even by such a structure, it is impossible to effectively prevent the elongation of the tube when the tube was applied to radiator hoses or the like.
On the other hand, in JP-A-7-214690, a radiator hose comprising an inner layer, an adhesive layer and an outer layer, wherein the outer layer is partly made of a glass fiber-reinforced thermoplastic resin, is proposed. This radiator hose has a corrugated portion, the outer layer of this corrugated portion contains no glass fibers, and each of straight tube portions located at both sides of the corrugated portion has an outer layer made of a glass fiber-reinforced thermoplastic resin.
However, in the above radiator hose, since the corrugated portion is made of only a thermoplastic resin containing no glass fibers, when the temperature of a coolant and the internal pressure are raised, it is impossible to prevent the elongation of the tube at the corrugated portion. Further, since the outer layers of the straight tube portions are made of a thermoplastic resin containing glass fibers, there is a problem such that when a resinous connector or the like is integrally formed with the tube at the end portion of the tube, no adequate bonding force between the connector and the hose can be obtained.
Accordingly, it is an object of the present invention to provide a corrugated resin tube having a corrugated portion, by which bending operation is made possible, vibration absorption property can be imparted, and at the same time, elongation due to heat or pressure can be effectively prevented.
In order to accomplish the above object, the first aspect of the present invention provides a corrugated resin tube which comprises, in at least one part of an axial direction of the tube, a corrugated portion having an undulated cross section along the axial direction, characterized in that the corrugated portion comprises at least one fiber-reinforced layer made of a thermoplastic resin or a thermoplastic elastomer, which contains inorganic fibers, and at least one resinous layer made of a thermoplastic resin or a thermoplastic elastomer, which contains no inorganic fibers or contains inorganic fibers in an amount less than the amount in the fiber-reinforced layer, wherein these layers are laminated and at least the outermost layer is the resinous layer.
According to the above invention, by providing as an inner layer a fiber-reinforced layer made of a thermoplastic resin or a thermoplastic elastomer, which contains inorganic fibers, when it is applied to e.g. radiator hoses, the flexibility of the corrugated portion is not substantially impaired, whereby the elongation of the corrugated portion can be prevented even under the high temperature and high pressure conditions, and the exposure of patterns of fibers at the outermost surface of the outer layer due to the presence of reinforcing fibers can be prevented, whereby appearance, hand feeling and texture can be improved. Further, since both fiber-reinforced layer and resinous layer are mainly made of a thermoplastic resin or a thermoplastic elastomer, these can be produced by a method capable of mass production such as extrusion molding.
The second aspect of the present invention provides the corrugated resin tube according to the first aspect, wherein the fiber-reinforced layer constitutes an intermediate layer and the resinous layers constitute inner and outer layers.
According to the second aspect of the present invention, since the corrugated tube is comprised of three layers wherein the intermediate layer constituted by the fiber-reinforced layer is sandwiched between the inner and outer layers constituted by resinous layers, not only the outermost surface but also the innermost surface are made smooth, whereby the resistance by an internal fluid can be reduced.
The third aspect of the present invention provides the corrugated resin tube according to the first aspect, wherein the resinous layer constitutes an outer layer and the fiber-reinforced layer constitutes an inner layer.
According to the third aspect of the present invention, since the corrugated tube is comprised of two layers i.e. the outer and inner layers, there is an advantage that the production can be made easily.
The fourth aspect of the present invention provides the corrugated resin tube according to any one of the first to third aspects, wherein the content of the inorganic fibers in the fiber-reinforced layer is from 5 to 20 wt %.
According to the fourth aspect of the present invention, prevention of elongation of the corrugated portion and impartation of flexibility are both possible under high temperature and high pressure conditions, and at the same time, bending property is not impaired.
The fifth aspect of the present invention provides the corrugated resin tube according to any one of the first to fourth aspects, wherein the thickness of the fiber-reinforced layer is from 30 to 70% of the whole thickness.
According to the fifth aspect of the present invention, elongation of the corrugated portion under high temperature and high pressure conditions can effectively be prevented, and at the same time, the bending property and vibration absorption at the corrugated portion are not impaired.
The sixth aspect of the present invention provides a corrugated resin tube according to any one of the first to fifth aspects, wherein at at least one end portion of the corrugated resin tube, a resinous connector is integrally molded with the corrugated resin tube by providing a gate near the circumference of an outermost layer constituted by the resinous layer and injection molding a resin for the connector to form a corrugated resin tube having the resinous connector integrally molded.
According to the sixth aspect of the present invention, it is possible to connect the corrugated tube to the pipes of engines or radiators with the resinous connector with one-touch operation, and by integrally molding the resinous connector with the tube, air tightness can be secured. Further, in the corrugated resin tube of the present invention, since the outermost layer is constituted by a resinous layer, when the resinous connector is integrally molded, adhesion between the connector and tube is excellent.
Moreover, when a gate is provided near the circumference of the outermost layer made of the resinous layer and a resin for a connector is injection molded, the fiber-reinforced layer provided at the inside of the outermost layer constitutes a layer wherein the inorganic fibers which are not susceptible to thermal effect at the level of 300xc2x0 C. are complicatedly entangled, whereby the shape can be kept without deformation, and it is possible to prevent the formation of a partial thin and weak portion in the tube wall.
The seventh aspect of the present invention provides the corrugated resin tube according to any one of the first to sixth aspects, wherein the corrugated resin tube is used for a radiator hose of an automobile.
According to the seventh aspect of the present invention, the radiator hose can be made light in weight and the operation efficiency for installation can be improved, and at the same time, even if the internal coolant becomes high in the temperature and pressure, it is possible to suppress the elongation and deformation of the hose.
In the present invention, as the inorganic fibers, glass fibers are preferably used. By using the glass fibers, the elongation of the corrugated portion under the high temperature and high pressure conditions can effectively be prevented, and at the same time, the material is inexpensive and therefore economical.
Further, as the thermoplastic resin used for the inner layer, an olefin type thermoplastic elastomer or thermoplastic resin is preferred. By using this material, flexibility can be imparted to the corrugated tube, and at the same time, solvent resistance to the coolant or the like containing e.g. ethylene glycol can be imparted.